In digital printing, especially electrostatic or electrophotographic printing, a latent electrostatic image is produced, which is developed by charged toner particles, which, in turn, are transferred to a print, for example, paper that receives the image. The image transferred to the print is fixed there by heating and softening of the toner and/or heating of the print. The toner particles are bonded to the print, and possibly also to each other, through and during this process.
Contactless fixing is desirable, in principle, to protect the printed image. Other advantages of contactless fixing are the avoidance of adhesive wear and increased service life of the employed device on this account, as well as improved reliability of the device.
The use of microwaves is considered, in particular, for this purpose. However, a problem with microwave fixing is that it is a heating method that heats the substrate in bulk and increasingly drives out moisture from the substrate at higher temperatures, especially above about 100° C. This drying, particularly during duplex printing, can lead to strong stress and drying of the substrate, which can cause additional problems in further processing of the print. In particular, drying of the substrate during the first pass through the microwave fixer has consequences for the second pass, since the moisture of the substrate plays a role during the heating process of the substrate by microwaves. It must also be kept in mind that during fixing of a duplex print image, the first-side image is melted again.